1. Field of the Invention
This invention relates to combustion chambers for gas turbine engines.
2. Description of the Prior Art
The emphasis today on the design and development of gas turbine engines for jet aircraft is towards pollution control, high temperature operation and reduction in engine weight without thrust penalties. Much of this design and development work is centered on the combustor section of the engine which, conventionally, has not provided the clean burning which is now desired. Furthermore, conventional combustors require a considerable axial length to perform the burning process; this increases the overall engine length, which of course results in an increase in engine weight.
Premixing of the fuel with the air is one technique which has been investigated to improve the combustion process. U.S. Pat. No. 2,999,359 to F. R. Murray shows such a technique in FIG. 2. One purpose of all the constructions shown in Murray is to create recirculating counter-rotating zones of combusting fuel and air within a primary combustion zone to improve combustion efficiency. Such recirculation increases the length of time the combusting fuel and air remains in the primary zone of combustion; this is undesirable from a pollution viewpoint since it increases the amounts of oxides of nitrogen produced within the combustion chamber.
Another fuel-air premixing system is shown in U.S. Pat. No. 3,055,179 to Lefebvre et al. In Lefebvre a stream of premixed fuel and air is injected into a secondary combustion zone through a plurality of auxiliary chutes, the mixture being ignited in the combustion zone by a pilot flame. The pilot flame extends from a toroidal pilot combustion chamber which encourages the recirculation of combustion gases within the toroidal zone. Again, as in Murray this recirculation increases the length of time the combusting fuel and air remains within high temperature regions and correspondingly increases the amounts of oxides of nitrogen produced within the combustion chamber.
A premix type of combustor system which has solved many of the above problems is described in copending patent application Ser. No. 336,578, PREMIX COMBUSTOR ASSEMBLY by J. E. Faucher, W. D. Roy and R. W. Koucky, filed on even date with the parent application from which the present application derives and having the same assignee as the present application.
Continuing efforts are being directed to the design of combustion chambers which are capable of fully combusting fuel within a limited axial length while minimizing the recirculation of combusting gases through high temperature zones which are capable of producing oxides of nitrogen. Additionally, these chambers must maintain flame stability during all engine operating conditions and have sufficiently high chamber exit temperatures to reduce unburned hydrocarbon emissions.